Yale Engineers Blow Mold Metal Alloys

A Yale University research group is blow molding miniatureresonators for microelectromechanical systems (MEMS)from a recently developed alloy of bulk metal glasses (BMG).

By blow molding the BMGs, the team was able to performshaping, joining and finishing in one step that took less than a minute.

"This could enable a whole new paradigm for shapingmetals," says JanSchroers, an associate professor of mechanical engineering at Yale. "The superior properties of BMGs relativeto plastics and typical metals, combined with the ease, economy and precisionof blow molding, have the potential to impact society just as much as thedevelopment of synthetic plastics and their associated processing methods havein the last century."

Bulk metallic glasses have a disordered atomic-scalestructure in contrast to most metals, which have a highly ordered arrangementof atoms.

Metallic glass was originally discovered atthe California Institute of Technology in 1960. A company called Liquidmetalsells titanium-based BMGs that are based on research at Caltech. More recently,amorphous metal has been produced that demonstrates strengths greater than traditionalsteel alloys.

Design News broke thestory last year that Apple has acquired an exclusive licenseto use Liquidmetal technology in personal electronics devices.

The Yale research shows potential for BMGs as a blow molded material,creating the possibility of different types of shapes than are possible ininjection molding or casting processes.

Stronger than steel
So far the Yale team has created a number of complex shapes,including seamless metallic bottles, watch cases, miniature resonators andbiomedical implants that can be molded in less than a minute and are twice asstrong as typical steel.

According to Schroers, the materials cost about the same ashigh-end steel. The alloys are made up of different metals, includingzirconium, nickel, titanium and copper.

The team blow molded the alloys at low temperatures and lowpressures, where the bulk metallic glass softens dramatically and flows aseasily as plastic but without crystallizing like regular metal. It's therelatively low temperatures and low pressures that allowed the team to shapethe BMGs with unprecedented ease, versatility and precision, Schroers said. Temperatureare around 430C, and pressures are also low, around 1 atmosphere.

In order to carefully control and maintain the idealtemperature for blow molding, the team shaped the BMGs in a vacuum or in fluid."Vacuum levels can be very low, just to reduce thermal conductivity of the environment,"says Schroers. "Lots of shapes do not require vacuum at all. The liquid processis for very complex shapes."

"The trick is to avoid friction typically present inother forming techniques," Schroers said. "Blow molding completelyeliminates friction, allowing us to create any number of complicated shapes,down to the nanoscale."

"This could enable a whole new paradigm for shapingmetals," Schroers said. "The superior properties of BMGs relative toplastics and typical metals, combined with the ease, economy and precision ofblow molding, have the potential to impact society just as much as thedevelopment of synthetic plastics and their associated processing methods havein the last century."

The Yale group has formed a company to commercialize thetechnology. Schroers told Design News this it would be "very realistic" for thecompany to making large volumes within two years.